The invention relates to improvements in methods of making recesses in at least partially metallic workpieces. More particularly, the invention relates to improvements in methods of making recesses (e.g., in the form of tapped or untapped blind holes or through holes) in workpieces which can be used in torque transmitting apparatus, for example, in the housings or covers of friction clutches for use in motor vehicles.
As a rule, a recess in a metallic workpiece is obtained by removing material from the workpiece, e.g., by resorting to a drill or to another suitable material removing tool. If the workpiece is to be provided with an internal thread, the treatment with a drill or with another material removing tool (which has been used to form a recess) must be followed by a treatment with a second tool which cuts a thread into the surface surrounding the recess. An internal thread is necessary if the recess is to receive a portion of an externally threaded shank forming part of a screw, bolt, spindle, feed screw, pin, post or the like. For example, it is often necessary to accurately center the workpiece relative to another part by resorting to so-called alignment, locating or centering pins (also called fixing or stead pins), dowel pins, drift pins or plugs, set pins or the like. A centering pin must be installed in a recess with a very high degree of accuracy in order to ensure that the thus coupled and centered parts are secured to each other with a minimum of play, i.e., within an acceptable range of tolerances. Such accuracy can be achieved by resorting to material removing and surface smoothing tools in the form of reamers or the like. All this contributes significantly to the cost of the workpieces, of the combinations of such workpieces with one or more additional workpieces as well as of the machines, apparatus or other devices in which the recessed workpieces are put to use. In addition, it is often difficult to dismantle an apparatus, machine or another device which employs one or more workpieces having one or more recesses which are obtained as a result of removal of metallic material from a blank or from a semifinished component of a friction clutch or the like.